Have a look at the overview article arXiv:1108.3269 "An introduction to quantum gravity" by Giampiero Esposito.
It lists 16 approaches to quantum gravity that were followed in the last 80 years - string theory is one of them. Then it lists their achievements. All are theoretical! Not a single of the achievements is a testable prediction.
Yep, quantum gravity is a dead alley. We all can stop reading gr-qc.